This disclosure pertains generally to microlithography methods and apparatus in which a charged particle beam such as an ion beam or electron beam is used for transferring a pattern to a suitable substrate. More specifically, the disclosure pertains to stage mechanisms for use in a charged-particle-beam (CPB) microlithography apparatus and in other apparatus that include a CPB optical system. In a CPB microlithography apparatus, the stage mechanisms are used for accurately and precisely positioning an object such as a reticle and/or lithographic substrate while imparting minimal disturbances to magnetic fields in the apparatus and suppressing reactive forces resulting from stage movements.
Microlithography is a key technique used in the manufacture of microelectronic devices such as semiconductor integrated circuits, displays, and micromachines. Currently, most microlithography is performed optically, using a beam of deep ultraviolet light. However, with the relentless demand for increased circuit density and smaller pattern linewidth, the inability of optical microlithography to continue to provide adequate pattern resolution is now quite apparent. Hence, much effort currently is being expended to develop a practical xe2x80x9cnext generationxe2x80x9d microlithography apparatus offering substantially finer pattern resolution.
In microlithography in general, the minimum obtainable pattern linewidth is a function of the wavelength of the lithographic energy beam. Hence, to obtain smaller linewidths, the wavelength of the energy beam has had to be correspondingly reduced. In optical microlithography, the smallest wavelengths currently being used are produced by excimer lasers (150-250 nm). These wavelengths can resolve pattern linewidths in the range of 0.18 to 0.25 xcexcm. Pattern resolution can be enhanced slightly, without reducing the wavelength, by controlling the beam-propagation atmosphere and employing certain techniques such as phase shifting and polarization control.
CPB microlithography, on the other hand, offers prospects of resolving pattern linewidths of about 70 nm, which substantially exceeds the resolution obtainable using excimer-laser wavelengths. However, even with CPB microlithography, achieving this level of performance will require that extreme measures be adopted to control extraneous influences on the charged particle beam that otherwise compromise the achievable pattern resolution.
In any type of microlithography apparatus, including CPB microlithography apparatus, it is necessary to move at least the lithographic substrate during exposure of each die on the substrate. In apparatus that project a pattern from a reticle, it also is necessary to move the reticle, usually in synchrony with movements of the substrate. Such controlled movements typically are made using a xe2x80x9cstage.xe2x80x9d The currently favored actuator for a stage in a microlithography apparatus is an electromagnetic linear motor, which is capable of achieving extremely accurate positioning and movements, as well as high movement velocity, required for performing microlithography of fine patterns. For obtaining highly accurate data regarding stage position, high-resolution laser interferometers typically are used. The actuators also include rigid, non-contacting air bearings to guide movements of the stage in the X and Y directions with essentially zero friction. Such stages can provide a positioning accuracy of a few nanometers.
In an electron-beam microlithography apparatus (as an exemplary CPB microlithography apparatus) the electron beam can be deflected in the electron-optical system at high velocity. These deflections can be made in real time to enable the electron-optical system to correct stage-position errors. As a result of this capability, stage-position accuracy can be relaxed somewhat, on the order of a few micrometers
A problem with using any type of electromagnetic actuator (e.g., linear motor) in a CPB optical system is that energization of the actuator generates fluctuating magnetic fields as the actuator moves. Any magnetic field has an effect on the trajectory of the charged particle beam in the CPB optical system. The sensitivity of the beam to magnetic fields is so exquisite that even a slight fluctuation in the magnetic field in the vicinity of the beam causes an unpredictable deflection and aberration of the beam, with a corresponding adverse effect on exposure accuracy and resolution.
In addition, whenever the actuator moves the stage, a reaction force is generated in accordance with Newton""s third law. The reaction force tends to be transmitted to the support structure of the microlithography apparatus, causing a corresponding vibration of the structure. These vibrations also are transmitted to the CPB optical system where they can cause placement errors of the transferred pattern and loss of contrast.
Conventional approaches to reducing these vibrations involve diversion of the vibrations to the floor or the like using a shock absorber that operates as a low-pass filter. Also, anti-vibration mechanisms based on the principle of conservation of momentum are utilized, such as disclosed in U.S. Pat. No. 5,815,246. Unfortunately, these various approaches are insufficient.
In view of the foregoing, the present invention provides, inter alia, stage devices that minimize magnetic-field disturbances of the charged particle beam, while more completely suppressing reaction forces due to stage actuation, thereby increasing the accuracy of stage-position control.
According to a first aspect of the invention, stage devices are provided. An embodiment of a stage device includes a base, a stage supported in a non-contacting manner relative to the base, and a pneumatic actuator. The pneumatic actuator is situated relative to the stage and base and is configured, whenever the pneumatic actuator is actuated by application of a gas pressure thereto, to move the stage relative to the base in a stage-movement direction so as to place the stage at a desired position relative to the base. The pneumatic actuator comprises (a) a moving element linked to the stage and a fixed element that supported in a non-contacting manner relative to the base, and (b) a momentum-conservation mechanism by which the fixed element can be driven as a counter mass in a direction opposite to the stage-movement direction in response to a driving-reaction force of the stage as applied to the moving element. The subject stage device can be, for example, a reticle stage or a substrate stage, for use in a charged-particle-beam (CPB) microlithography apparatus.
Another embodiment of a stage device includes a base, a stage, an X-direction driver, and a Y-direction driver. The stage is supported in a non-contacting manner relative to the base. The X-direction driver comprises a respective pneumatic actuator that is situated relative to the stage and base so as to move the stage in the X direction relative to the base. Similarly, the Y-direction driver comprises a respective pneumatic actuator that is situated relative to the stage and base so as to move the stage in the Y direction relative to the base. Each pneumatic actuator comprises: (a) a respective moving element linked to the stage side, (b) a respective fixed element supported in a non-contacting manner relative to the base, and (c) a momentum-conservation mechanism by which the respective fixed element can be driven as a counter mass in a direction opposite to the stage-movement direction in response to a driving-reaction force of the stage as applied to the respective moving element. In this embodiment each fixed element desirably is supported in a non-contacting manner relative to the base by a respective gas bearing comprising a differential exhaust mechanism. Furthermore, each fixed element can include a respective actuator for correcting a stroke of the respective fixed element.
According to another aspect of the invention, microlithography apparatus are provided that comprise at least one stage device as summarized above. The microlithography apparatus generally can include an illumination-optical system and a projection-optical system situated downstream of the illumination-optical system. The stage device(s) in such apparatus can be a reticle stage and/or a substrate stage.
According to another aspect of the invention, methods are provided, in the context of holding an object on a stage relative to a base, for moving and positioning the object (while being held on the stage) relative to the base. An embodiment of such a method comprises linking the stage to the base by a pneumatic actuator comprising a moving element linked to the stage and a fixed element linked to the moving element. The fixed element is supported in a non-contacting manner relative to the base. The stage is driven pneumatically so as to undergo movement in a stage-movement direction relative to the base. In response to a driving-reaction force of the stage as applied to the moving element in response to driving the stage, the fixed element is driven as a counter mass in a direction opposite to the stage-movement direction. Desirably, the fixed element is driven pneumatically.
In another embodiment of a method, the stage is linked to the base by an X-direction pneumatic actuator and a Y-direction pneumatic actuator. The X-direction pneumatic actuator comprises a respective moving element linked to the stage and a respective fixed element linked to the respective moving element, wherein the respective fixed element is supported in a non-contacting manner relative to the base. The Y-direction pneumatic actuator comprising a respective moving element linked to the stage and a respective fixed element linked to the respective moving element, wherein the respective fixed element is supported in a non-contacting manner relative to the base. The X-direction pneumatic actuator and Y-direction pneumatic actuator are driven as required to move the stage in respective X and Y stage-movement directions in an XY plane relative to the base. In response to a driving-reaction force of the stage as applied to the moving element in response to moving the stage, the fixed elements are driven (e.g., pneumatically) as respective counter masses in respective directions opposite to the stage-movement directions.
In the methods and devices summarized above that achieve movement and positioning of the stage in the XY plane, by configuring the X- and Y-direction actuators as pneumatic actuators rather than electromagnetic actuators, the problem of magnetic-field fluctuations especially near a charged particle beam is eliminated.
Conventionally, stage structures capable of movement in both the X and Y directions tend to be large and massive. Hence, reaction forces acting on the fixed elements in such devices also tend to be large. In methods and devices as summarized above, the stage and the fixed element(s) are supported relative to the base plate in respective non-contacting manners. As a result, the respective fixed elements serve as respective counter masses. This prevents the reaction forces, generated as the stage is being driven, from being transmitted outside the stage, even if the structure of the stage is relatively large.
In any of the devices summarized above, each fixed element desirably is supported relative to the base plate in a non-contacting manner. This desirably is achieved using respective air bearings equipped with differential exhaust mechanisms. A gas bearing has extremely low contact resistance and creates almost no magnetic fields. Consequently, gas bearings (as used in the stage devices described herein) are superior from the standpoints of both stage controllability and absence of harmful effects on a nearby CPB optical system. Also, providing each gas bearing with a respective differential exhaust mechanism reduces air leakage, thereby allowing the stage devices to be used in a vacuum chamber.
Further with respect to the stage devices disclosed herein, the moving elements (e.g., air sliders) linked to the stage desirably are supported by respective non-contacting gas bearings (each having a respective differential exhaust mechanism) relative to the respective fixed element.
When the stage devices as disclosed herein are used in a vacuum environment where air resistance does not exist, the principle of conservation of momentum operates almost perfectly.
The foregoing and additional features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.